This invention was made with Government support under Grants Nos. ECS-8815775 and ECS-8805866 awarded by the National Science Foundation. The Government has certain rights in the invention.
The present invention relates, in general, to a process for producing microdynamic structures and to the structures produced by that process, and more particularly is directed to the fabrication of three-dimensional tungsten cantilever beams on a substrate.
The field of micro-electromechanical systems is a new, emerging technology which has as its goal the integration of electronic circuits, sensors, and electromechanical motion devices to build complete electromechanical systems on a micrometer scale. Recent research interest in such systems has focused on the fabrication of microactuators and micromotors which have applications as micromechanical positioners, robotic actuators, and microprobes. Recent research has shown that rotating and sliding structures can be fabricated using modified silicon processing. To date, research emphasis has been directed toward the fabrication of movable microstructures using polycrystalline silicon with sacrificial layers which, upon removal, releases the microstructures for motion. One disadvantage of the present technology is that the deposition of only relatively thin layers of polysilicon are practical, and thus the silicon micromechanical structures are usually planar structures that are not easily extended to three dimensions. Furthermore, these structures are fragile and require many process steps to create a movable, free structure.
Silicon-based electrostatic actuators and electrostatic motors are crucial to the construction of integrated micro-electromechanical systems. However, attempts to achieve motion in microdevices have been impeded by the complexity of the processes required to build three dimensional structures, and by the forces that make materials stick together upon contact, to impede or prevent relative motion. Four major challenges to the production of a working micro motor have been identified as being the control of friction and wear; the control of surface charges and interfacial forces; the development of a process that produces movable parts; and the control of stress, especially in the movable parts. The first two challenges require considerable experimental research to measure and identify the controlling parameters, while the third and fourth challenges are very closely related since a movable structure must conform to a designed shape, whereas stress plays a major role in distorting a structure when it is released from a mold.